-LRB- CNN -RRB- -- Spc. Ivan Lopez vented about a range of subjects on Facebook before his shooting rampage at Fort Hood in Texas , including his outrage at Adam Lanza 's mass school shooting in Connecticut .

He wrote of experiencing overpowering fear after an insurgent attack in Iraq and the hatred that consumed him after getting `` robbed . ''

Lopez took his own .45 - caliber handgun onto the sprawling post Wednesday and killed three people and wounded 16 more before taking his own life , according to authorities .

They are trying to piece together what in his background and psychiatric treatment could have triggered a new round of bloodshed at the same Killeen post where an officer killed 13 people in 2009 .

A 34-year-old Iraq war veteran with a history of depression and anxiety , Lopez was being evaluated for post-traumatic stress disorder before his shooting spree . He arrived at the post in February after being transferred from Fort Bliss in El Paso .

His Facebook posts , which were obtained from a Lopez family friend , appeared under the account name of `` Ivan Slipknot , '' a reference to a heavy metal band . A family spokesman confirmed the account belonged to Lopez .

It is unclear whether his posts might help explain his mental state or a possible motive in the shootings . Authorities have said the motive is not known .

`` Given that the alleged shooter is deceased , the possibility does exist that we may never know exactly why the alleged shooter did what he did , '' said Chris Grey , a spokesman for the U.S. Army Criminal Investigation Command .

In early March , around the time investigators said he purchased the .45 - caliber pistol used in the shootings , Lopez wrote : `` My spiritual peace has just gone . Full of hate . Now I think I 'll be damned . Last night I was robbed and I 'm pretty sure there were 2 skinny ones . Green light and thumb down . That easy . ''

The details of the robbery are unknown . Killeen , Texas , police said the records department was closed Saturday .

In another Facebook post , Lopez talked about Lanza , 20 , who killed his mother , Nancy , before fatally shooting 20 children , six staff members and himself at Sandy Hook Elementary School in Newtown in December 2012 .

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Lopez wrote that Lanza `` pretends to be a victim of a mental illness followed by addiction to violent video games '' and that the shooter sought `` international attention '' and a `` minute of fame as a villain . ''

He added , `` It is stupid to me that anyone can have easy access to a powerful weapon without being mentally evaluated . This makes the government indirect accomplice ... These bastards have perfected their way of attacking studying previous massacres to gain publicity and their minute of fame as a villain . But thanks to Hollywood and the sensational profiling by the media -LSB- they -RSB- give more power to those intelligent cowards . ''

Another post dealt with his time in Iraq : `` Celebrating life . It has been exactly 1 year and 2 days since left Iraq seeing in Fallujah the most brutal explosion ... I was left paralyzed and started a discussion over the radio ... I was only focused on breathing deeply so that I do n't lose focus and continue the mission . -LSB- Those -RSB- were hours of agony waiting for an attack by the insurgency but we were able to exit Fallujah all alive . I was in vehicle # 6 . The worst was that # 5 was a diesel truck , the perfect target . And I was only thinking about getting back with my family . ''

Lopez added : `` To be in the line of fire is f ----- up but even more f ----- is the suffering of the families . ''

Lt. Gen. Mark Milley , the post 's commanding general , said Lopez did not experience direct combat in Iraq .

`` So far , we have not discovered any specific traumatic event , wounds received in action , contact with the enemy or anything else specific that he may have been exposed to while deployed , '' the general said .

Grey said authorities had `` credible information '' that Lopez `` was involved in a verbal altercation with soldiers from his unit just prior to him allegedly opening fire . ''

Messages left Saturday by CNN for Grey about the Facebook posts were not immediately returned .

In a statement Friday , Lopez ' father , also named Ivan , asked for prayers for all those affected . He described the soldier as `` a calm family man '' and `` a good son . ''

`` My son could not have been in his right mind , '' he said . `` He was not like this . ''

Lopez was Iraq vet being treated for mental health issues

Looking for clues into GI 's actions , motive

Before Wednesday 's shooting , Lopez stopped at the post 's personnel office to pick up a leave form , according to the sister of one of the soldiers injured in the attack .

Armetra Otis , sister of Sgt. Jonathan Westbrook , said on CNN 's `` The Lead '' that her brother `` was at work and a guy came in and asked for a leave form . ''

The soldier was told he would have to come back later , Otis said .

`` And apparently I guess he did n't want to hear that , so he came back and just opened fire , '' Otis said .

Westbrook was shot four times , but released from a hospital Friday , his sister said .

Law enforcement sources told CNN that investigators were searching for possible motives , including whether Lopez was angry over canceled leave .

If Lopez sought a leave this week , it would n't be his first .

Glidden Lopez Torres , a family spokesman , said Lopez ' mother , Carmen , an emergency room nurse in their hometown , died of a heart attack in November . A month earlier , Lopez ' grandfather had died in Guayanilla , a tight knit seaside community of 22,000 on the southern coast of Puerto Rico .

The spokesman , not related to the soldier , said Lopez attended the funeral but was disappointed that it took about five days for his 24-hour leave to be approved by the military .

In Friday 's statement , the soldier 's father said his son 's medical treatment , the recent deaths of his mother and grandfather and changes related to a transfer of military installations `` surely affected his condition . ''

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CNN 's Devna Shukla contributed to this report .

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Spc. Ivan Lopez , before Fort Hood attack : `` My spiritual peace has just gone ''

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Lopez received treatment for depression , anxiety

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He killed 3 , wounded 16 before taking his own life

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`` It is stupid to me that anyone can have easy access to a powerful weapon without being mentally evaluated ''